1. Field of the Invention
The present invention relates to an atomizer, in particular to a nozzle plate with a multi-curved surface structure having a geometric pattern radially or circularly arranged at the center of the nozzle plate, and an atomizing module using the nozzle plate.
2. Description of the Related Art
In general, an atomizer including an ultrasonic atomizer is made of a piezoelectric (PZT) ceramic material such as lead zirconate titanate. After a voltage is supplied, the ceramic material and a bundled metal back panel may be expanded, contracted or deformed, and energy is transmitted in form of waves, so that a vibration produced falls within a nanometer scale when the atomizer is operated at a frequency of ultrasonic waves, and the vibration can be controlled by the input voltage. The vibration produced by the piezoelectric material can be used for transmitting the ultrasonic waves to a nozzle plate, and a liquid near a nozzle can be divided into smaller molecules by the action of Rayleigh waves or surface waves to facilitate the spray and atomization of the liquid.
With reference to FIGS. 1 and 2 for an exploded view and a schematic view of a conventional atomizing device respectively, the conventional atomizing device 1 comprises an atomizing module 11 and a cavity 12. The atomizing module 11 includes a piezoelectric circular plate 113, a nozzle plate 112 and a braking circular plate 111. The nozzle plate 112 is substantially in a circular disc shape and includes a plurality of firing holes 1121 formed thereon, and the nozzle plate 112 is clamped between the piezoelectric circular plate 113 and the braking circular plate 111. The atomizing module 11 is installed on a side of the cavity 12. When the piezoelectric circular plate 113 is driven by a voltage to start vibrating, the vibration wave is transmitted to the nozzle plate 112, so that the liquid near the firing holes 1121 can be converted into water molecules.
However, the nozzle plate 112 is in a circular flat shape, so that it has the following drawbacks:
1. When the piezoelectric circular plate 113 vibrates, the produced vibration waves are transmitted in a direction from the external periphery of the nozzle plate 112 to the center of the nozzle plate 112, so that too much vibration energy is concentrated at the center of the nozzle plate 112, and the center area of the nozzle plate 112 has a too-large amplitude, and thus resulting in cracking or breaking the nozzle plate 112 easily by stress, and shortening the service life of the nozzle plate.
2. The vibration energy is concentrated at the center of the nozzle plate 112, so that an atomizing area is formed at the center of the nozzle plate 112 only. Since the atomizing area is situated at the center of the nozzle plate 112, an effective use of the firing holes 1121 of the nozzle plate 112 causes a poor atomization.
3. The atomization process requires a liquid-gas exchange to maintain a balance between internal and external pressures of an atomizing device. Due to the too-small atomizing area, the spray is unstable, and the flow of the sprayed liquid is unsteady.
4. The atomizing area is concentrated at the center area, and the molecular density of the atomized liquid is too large, so that liquid drops will collide easily to form liquid drops of a large diameter and lower the atomization efficiency.
With reference to FIGS. 3 to 6 for an exploded view of a conventional mist generator, a cross-sectional view of the conventional mist generator, a schematic view operating the conventional mist generator, and a schematic view of an atomizing area respectively, a mist generator as disclosed in R.O.C. Pat. No. I331055 is provided for overcoming the aforementioned drawbacks, wherein the mist generator 2 is used for atomizing a liquid and applied to an atomizing device having a through hole. The mist generator 2 comprises a braking circular plate 21, a nozzle plate 22, a piezoelectric circular plate 23 and a cavity 24. The nozzle plate 22 includes a plurality of firing holes 221 and is clamped between the braking circular plate 21 and the piezoelectric circular plate 23, and an atomizing area 223 is formed at the center of the nozzle plate 22. Wherein, a hemispherical curved surface structure 222 is formed at the center of the nozzle plate 22.
Although the design of the hemispherical surface structure can achieve the effects of improving the atomization of the prior art, reducing the stress concentrated at the center of the nozzle plate 22, and producing a larger atomizing area 223 theoretically, yet the practical application of mist generator 2 still has the following drawbacks:
1. When the nozzle plate 22 with the hemispherical surface structure is manufactured, the processing depth is inversely proportional to the curvature of the hemispherical surface due to the features of the manufacturing materials and properties. To achieve the effect of improving the atomization, the manufacturing depth at the center of the nozzle plate 22 must be equal to a certain depth. The smaller the curvature of the hemispherical surface, the easier is the manufacture for the required depth. To achieve the depth for the best atomization performance of the hemispherical surface, it is necessary to reduce the effective atomization range. In order to increase the effective atomization range, the radius of curvature for the manufacture must be increased. As a result, the manufacturing depth becomes shallow, and the atomization performance becomes lower. If it is necessary to achieve a smaller radius of curvature under the condition of the same size, a too-large stress will be exerted onto the nozzle plate 22 easily, and the structure will exceed the limit of deformation and end up with a crack or break, or the yield strength drops, so that the nozzle plate will be cracked or broken easily after the nozzle plate is vibrated for several times.
2. Due to the properties of the material of the nozzle plate 22, a greater diameter of the manufactured hemispherical surface will decrease the structural tension, weaken the inputted force and reduce the low-frequency resonance resisting capability, so that noises may be produced easily.
3. The packaged structure with this atomization method can clamp the nozzle plate 22 stably, and the internal diameter of the braking circular plate 21 is generally smaller than the internal diameter of the piezoelectric circular plate 23, and a vast majority of the vibration energies is transmitted to the nozzle plate 22, and the peripheral vibration area of the hemispherical surface design incapable of atomizing a liquid can be eliminated, and a portion of the firing holes 221 of the nozzle plate 22 has a lower utility rate, so that the atomizing area and the atomization on the nozzle plate 22 will be reduced. In addition, when the piezoelectric circular plate 21 is operated, adhesive is applied between layers of the piezoelectric circular plate 21, the nozzle plate 22 and the braking circular plate 23 and the force applying arms are of different lengths, the adhesion between components will be malfunctioned easily.
4. In the design of the hemispherical surface structure of the conventional nozzle plate, most of the transmitted energies of vibration waves are still concentrated at the center area, so that the micro holes formed at the center area have effective actions, but the vibration energy at the micro holes formed at the peripheral area is insufficient for an effective use, and the atomizing area cannot meet the design requirement.